When reading popular fiction, there is this combination of two factors that I really, really don't like to see.
Characters who meet stereotyped expectations can be annoying, but they won't usually make me stop reading.
Well established characters behaving way out of type can also be annoying; but again, won't necessarily make me stop reading.
However. When a well established character, with an established personality and beliefs, suddenly starts conforming to a stereotype that is completely out of character for them, it's usually time for me to swear out loud and put the book down. That just hurts. I haven't seen many examples of it, but the ones I have seen are all memorable cases that I wouldn't read again.